Minimally invasive surgery (MIS) is often preferred over traditional open surgery due to the reduced post-operative recovery time and minimal scarring associated therewith. Laparoscopic surgery is one type of MIS procedure in which one or more small incisions are formed in the abdomen and a trocar is inserted through each incision to form a pathway that provides access to the abdominal cavity. The trocar is used to introduce various instruments and tools into the abdominal cavity, as well as to provide insufflation to elevate the abdominal wall above the organs. The instruments and tools can be used to engage and/or treat tissue in a number of ways to achieve a diagnostic or therapeutic effect. Endoscopic surgery is another type of MIS procedure in which elongate flexible shafts are introduced into the body through a natural orifice.
Conventional MIS devices include a handle, an elongate shaft, and an end effector at the distal end. Motion of the end effector is typically limited to four degrees of freedom: (1) rotation of the end effector about its longitudinal axis, which is achieved by rotating the entire device relative to the trocar, (2) in-out translational movement of the end effector, which is achieved by sliding the entire device longitudinally relative to the trocar, (3) up-down translational movement of the end effector, which is achieved by angling the device and trocar relative to the patient, and (4) left-right translational movement of the end effector, which is also achieved by angling the device and trocar relative to the patient. Some MIS devices also include a wrist joint proximal to the end effector which provides two additional degrees of freedom: (5) up-down pivot movement of the end effector and (6) left-right pivot movement of the end effector.
Conventional MIS devices suffer from a number of disadvantages. For example, the trocar angling that is required to achieve up-down translational movement and left-right translational movement of the end effector places a significant amount of strain on the incision in which the trocar is inserted, which can cause increased trauma and inadvertent release of insufflation gas. Moreover, this trocar angling makes it difficult if not impossible to operate effectively with two devices inserted into the same incision, or inserted into incisions that are in close proximity to each other, as the elongate shafts of the two devices interfere with one another when the devices are angled. Thus, in order to maintain optimum maneuverability, multiple incisions are used when multiple conventional MIS devices must be employed simultaneously, which further increases patient trauma and scarring.
By way of further example, controlling conventional MIS systems can be cumbersome, and motion error introduced by such devices makes end effector movement seem unnatural to the user. In addition, shear forces associated with conventional MIS instruments can be high, leading to increased user fatigue.
Various robotic systems have been developed to assist in MIS procedures. Robotic systems generally operate by translating user motion of a master device into control signals for driving a plurality of servos. The servos in turn selectively actuate a slave device to impart the desired motion thereto. One drawback with robotic systems, however, is the loss of a direct mechanical linkage between the user and the tissue or object being manipulated. With robotic systems, there can be no true force feedback given to the user. Another drawback is the high expense associated with such systems. Furthermore, robotic systems suffer from the same trocar angling requirements as conventional MIS devices.
Accordingly, there remains a need for improved methods and devices for controlling movement of an end effector assembly on a distal end of a surgical device.